Conditional handover and radio link failure timer interaction

ABSTRACT

Certain aspects of the present disclosure provide techniques for handling a radio link failure timer in the presence of a conditional handover command. A method that may be performed by a user equipment (UE) includes receiving, from a serving cell, a conditional handover command for handing over the UE to a target neighbor cell, wherein the conditional handover command includes one or more triggering conditions for executing a handover to a candidate target cell; monitoring one or more first signals from the candidate target cell for the one or more triggering conditions; and performing one of: stopping a timer based on performing a conditional handover to the target candidate cell; or detecting a timer has expired while monitoring the one or more first signals from the candidate target cell for the one or more triggering conditions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of and priority to U.S. ProvisionalApplication No. 62/890,457, filed Aug. 22, 2019, which is herebyassigned to the assignee hereof and hereby expressly incorporated byreference herein in their entireties as if fully set forth below and forall applicable purposes.

FIELD OF THE DISCLOSURE

Aspects of the present disclosure relate to wireless communications, andmore particularly, to techniques for handling a radio link failure timerin the presence of a conditional handover command.

DESCRIPTION OF RELATED ART

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,broadcasts, etc. These wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources (e.g., bandwidth,transmit power, etc.). Examples of such multiple-access systems include3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE)systems, LTE Advanced (LTE-A) systems, code division multiple access(CDMA) systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, orthogonal frequency divisionmultiple access (OFDMA) systems, single-carrier frequency divisionmultiple access (SC-FDMA) systems, and time division synchronous codedivision multiple access (TD-SCDMA) systems, to name a few.

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. New radio (e.g., 5G NR) is an exampleof an emerging telecommunication standard. NR is a set of enhancementsto the LTE mobile standard promulgated by 3GPP. NR is designed to bettersupport mobile broadband Internet access by improving spectralefficiency, lowering costs, improving services, making use of newspectrum, and better integrating with other open standards using OFDMAwith a cyclic prefix (CP) on the downlink (DL) and on the uplink (UL).To these ends, NR supports beamforming, multiple-input multiple-output(MIMO) antenna technology, and carrier aggregation.

However, as the demand for mobile broadband access continues toincrease, there exists a need for further improvements in NR and LTEtechnology. Preferably, these improvements should be applicable to othermulti-access technologies and the telecommunication standards thatemploy these technologies.

SUMMARY

The systems, methods, and devices of the disclosure each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this disclosure as expressedby the claims which follow, some features will now be discussed briefly.After considering this discussion, and particularly after reading thesection entitled “Detailed Description” one will understand how thefeatures of this disclosure provide advantages that include improvedhandling for radio link failure timers in the presence of a conditionalhandover command.

Certain aspects provide a method for wireless communication by a userequipment (UE). The method generally includes communicating with aserving cell over a communication link; monitoring at least one of oneor more signals from the serving cell or one or more signals from one ormore candidate neighbor cells based, at least in part, on one or moremeasurement events configured in one or more measurement objects;detecting the one or more measurement events based on the monitoring,wherein a timer is configured for the one or more measurement events inthe one or more measurement objects; starting the timer based ondetecting the one or more measurement events; transmitting a measurementreport based on the detected one or more measurement events; receiving aconditional handover command for handing the UE over to a candidatetarget cell of the one or more candidate neighbor cells, wherein theconditional handover command includes one or more triggering conditionsfor executing a conditional handover to the candidate target cell; andstopping the timer based on the received conditional handover command.

Certain aspects provide an apparatus for wireless communication by auser equipment (UE). The apparatus generally includes at least oneprocessor configured to: communicate with a serving cell over acommunication link; monitor at least one of one or more signals from theserving cell or one or more signals from one or more candidate neighborcells based, at least in part, on one or more measurement eventsconfigured in one or more measurement objects; detect the one or moremeasurement events based on the monitoring, wherein a timer isconfigured for the one or more measurement events in the one or moremeasurement objects; start the timer based on detecting the one or moremeasurement events; transmit a measurement report based on the detectedone or more measurement events; receive a conditional handover commandfor handing the UE over to a candidate target cell of the one or morecandidate neighbor cells, wherein the conditional handover commandincludes one or more triggering conditions for executing a conditionalhandover to the candidate target cell; and stop the timer based on thereceived conditional handover command. The apparatus also generallyincludes a memory coupled with the at least one processor.

Certain aspects provide an apparatus for wireless communication by auser equipment (UE). The apparatus generally includes means forcommunicating with a serving cell over a communication link; means formonitoring at least one of one or more signals from the serving cell orone or more signals from one or more candidate neighbor cells based, atleast in part, on one or more measurement events configured in one ormore measurement objects; means for detecting the one or moremeasurement events based on the monitoring, wherein a timer isconfigured for the one or more measurement events in the one or moremeasurement objects; means for starting the timer based on detecting theone or more measurement events; means for transmitting a measurementreport based on the detected one or more measurement events; means forreceiving a conditional handover command for handing the UE over to acandidate target cell of the one or more candidate neighbor cells,wherein the conditional handover command includes one or more triggeringconditions for executing a conditional handover to the candidate targetcell; and means for stopping the timer based on the received conditionalhandover command.

Certain aspects provide a non-transitory computer-readable medium forwireless communication by a user equipment (UE). The apparatus generallyincludes instructions that, when executed by at least one processor,cause the at least one processor to: communicate with a serving cellover a communication link; monitor at least one of one or more signalsfrom the serving cell or one or more signals from one or more candidateneighbor cells based, at least in part, on one or more measurementevents configured in one or more measurement objects; detect the one ormore measurement events based on the monitoring, wherein a timer isconfigured for the one or more measurement events in the one or moremeasurement objects; start the timer based on detecting the one or moremeasurement events; transmit a measurement report based on the detectedone or more measurement events; receive a conditional handover commandfor handing the UE over to a candidate target cell of the one or morecandidate neighbor cells, wherein the conditional handover commandincludes one or more triggering conditions for executing a conditionalhandover to the candidate target cell; and stop the timer based on thereceived conditional handover command.

Certain aspects provide a method for wireless communication by a userequipment (UE). The method generally includes receiving, from a servingcell, a conditional handover command for handing over the UE to a targetneighbor cell, wherein the conditional handover command includes one ormore triggering conditions for executing a handover to a candidatetarget cell; monitoring one or more first signals from the candidatetarget cell for the one or more triggering conditions; and performingone of: stopping a timer based on performing a conditional handover tothe target candidate cell; or detecting a timer has expired whilemonitoring the one or more first signals from the candidate target cellfor the one or more triggering conditions.

Certain aspects provide an apparatus for wireless communication by auser equipment (UE). The apparatus generally includes at least oneprocessor configured to: receive, from a serving cell, a conditionalhandover command for handing over the UE to a target neighbor cell,wherein the conditional handover command includes one or more triggeringconditions for executing a handover to a candidate target cell; monitorone or more first signals from the candidate target cell for the one ormore triggering conditions; and perform one of: stopping a timer basedon performing a conditional handover to the target candidate cell; ordetecting a timer has expired while monitoring the one or more firstsignals from the candidate target cell for the one or more triggeringconditions. The apparatus also generally includes a memory coupled withthe at least one processor.

Certain aspects provide an apparatus for wireless communication by auser equipment (UE). The apparatus generally includes means forreceiving, from a serving cell, a conditional handover command forhanding over the UE to a target neighbor cell, wherein the conditionalhandover command includes one or more triggering conditions forexecuting a handover to a candidate target cell; means for monitoringone or more first signals from the candidate target cell for the one ormore triggering conditions; and means for performing one of: stopping atimer based on performing a conditional handover to the target candidatecell; or detecting a timer has expired while monitoring the one or morefirst signals from the candidate target cell for the one or moretriggering conditions.

Certain aspects provide a non-transitory computer-readable medium forwireless communication by a user equipment (UE). The apparatus generallyincludes instructions that, when executed by at least one processor,cause the at least one processor to: receive, from a serving cell, aconditional handover command for handing over the UE to a targetneighbor cell, wherein the conditional handover command includes one ormore triggering conditions for executing a handover to a candidatetarget cell; monitor one or more first signals from the candidate targetcell for the one or more triggering conditions; and perform one of:stopping a timer based on performing a conditional handover to thetarget candidate cell; or detecting a timer has expired while monitoringthe one or more first signals from the candidate target cell for the oneor more triggering conditions.

To the accomplishment of the foregoing and related ends, the one or moreaspects comprise the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe appended drawings set forth in detail certain illustrative featuresof the one or more aspects. These features are indicative, however, ofbut a few of the various ways in which the principles of various aspectsmay be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the drawings. It is to be noted, however, thatthe appended drawings illustrate only certain typical aspects of thisdisclosure and are therefore not to be considered limiting of its scope,for the description may admit to other equally effective aspects.

FIG. 1 is a block diagram conceptually illustrating an exampletelecommunications system, in accordance with certain aspects of thepresent disclosure.

FIG. 2 is a block diagram conceptually illustrating a design of anexample a base station (BS) and user equipment (UE), in accordance withcertain aspects of the present disclosure.

FIG. 3 illustrates an example of a decision flow for early RLFdeclaration in accordance with aspects of the present disclosure.

FIG. 4 is a flow diagram illustrating example operations for wirelesscommunication by a UE, in accordance with certain aspects of the presentdisclosure.

FIG. 5 illustrates a call-flow diagram showing example operations forhandling the case where no conditional handover configuration is activein the UE before triggering of the RLF timer, in accordance with certainaspects of the present disclosure.

FIG. 6 is a flow diagram illustrating example operations for wirelesscommunication by a UE, in accordance with certain aspects of the presentdisclosure.

FIG. 7 illustrates a call-flow diagram showing example operations forhandling the case where conditional handover configuration is active inthe UE before triggering of the RLF timer, in accordance with certainaspects of the present disclosure.

FIG. 8 illustrates a communications device that may include variouscomponents configured to perform operations for the techniques disclosedherein in accordance with aspects of the present disclosure.

FIG. 9 illustrates a communications device that may include variouscomponents configured to perform operations for the techniques disclosedherein in accordance with aspects of the present disclosure.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in one aspectmay be beneficially utilized on other aspects without specificrecitation.

DETAILED DESCRIPTION

Aspects of the present disclosure provide apparatus, methods, processingsystems, and computer readable mediums for handling a radio link failuretimer in the presence of a conditional handover command. For example, aconditional handover is a type of handover in which the serving cellprovides the UE with a handover command that includes one or moretriggering conditions for autonomously initiating a handover to acandidate neighbor cell. However, it is currently unspecified howconditional handovers should interact with the radio link failure (RLF)timers. Thus, aspects of the present disclosure provide techniques forhandling an RLF timer (e.g., starting, stopping, expiry behavior) in thepresence of a conditional handover command.

As noted, the following description provides examples of handling aradio link failure timer in the presence of a conditional handovercommand in communication systems, and is not limiting of the scope,applicability, or examples set forth in the claims. Changes may be madein the function and arrangement of elements discussed without departingfrom the scope of the disclosure. Various examples may omit, substitute,or add various procedures or components as appropriate. For instance,the methods described may be performed in an order different from thatdescribed, and various steps may be added, omitted, or combined. Also,features described with respect to some examples may be combined in someother examples. For example, an apparatus may be implemented or a methodmay be practiced using any number of the aspects set forth herein. Inaddition, the scope of the disclosure is intended to cover such anapparatus or method which is practiced using other structure,functionality, or structure and functionality in addition to, or otherthan, the various aspects of the disclosure set forth herein. It shouldbe understood that any aspect of the disclosure disclosed herein may beembodied by one or more elements of a claim. The word “exemplary” isused herein to mean “serving as an example, instance, or illustration.”Any aspect described herein as “exemplary” is not necessarily to beconstrued as preferred or advantageous over other aspects.

In general, any number of wireless networks may be deployed in a givengeographic area. Each wireless network may support a particular radioaccess technology (RAT) and may operate on one or more frequencies. ARAT may also be referred to as a radio technology, an air interface,etc. A frequency may also be referred to as a carrier, a subcarrier, afrequency channel, a tone, a subband, etc. Each frequency may support asingle RAT in a given geographic area in order to avoid interferencebetween wireless networks of different RATs. In some cases, a 5G NR RATnetwork may be deployed.

FIG. 1 illustrates an example wireless communication network 100 inwhich aspects of the present disclosure may be performed. For example,the wireless communication network 100 may be an NR system (e.g., a 5GNR network).

As illustrated in FIG. 1, the wireless communication network 100 mayinclude a number of base stations (BSs) 110 a-z (each also individuallyreferred to herein as BS 110 or collectively as BSs 110) and othernetwork entities. A BS 110 may provide communication coverage for aparticular geographic area, sometimes referred to as a “cell”, which maybe stationary or may move according to the location of a mobile BS 110.In some examples, the BSs 110 may be interconnected to one anotherand/or to one or more other BSs or network nodes (not shown) in wirelesscommunication network 100 through various types of backhaul interfaces(e.g., a direct physical connection, a wireless connection, a virtualnetwork, or the like) using any suitable transport network. In theexample shown in FIG. 1, the BSs 110 a, 110 b and 110 c may be macro BSsfor the macro cells 102 a, 102 b and 102 c, respectively. The BS 110 xmay be a pico BS for a pico cell 102 x. The BSs 110 y and 110 z may befemto BSs for the femto cells 102 y and 102 z, respectively. A BS maysupport one or multiple cells. The BSs 110 communicate with userequipment (UEs) 120 a-y (each also individually referred to herein as UE120 or collectively as UEs 120) in the wireless communication network100. The UEs 120 (e.g., 120 x, 120 y, etc.) may be dispersed throughoutthe wireless communication network 100, and each UE 120 may bestationary or mobile.

According to certain aspects, the BSs 110 and/or UEs 120 may beconfigured for handling a radio link failure (RLF) timer in the presenceof a conditional handover command as explained below. For example, asshown in FIG. 1, the UE 120 a includes an RLF manager 122. The RLFmanager 122 may be configured, in some cases, to perform the operationsillustrated in one or more of FIGS. 4-7 as well as other operationsdescribed herein for handling a radio link failure timer in the presenceof a conditional handover command, in accordance with aspects of thepresent disclosure.

Wireless communication network 100 may also include relay stations(e.g., relay station 110 r), also referred to as relays or the like,that receive a transmission of data and/or other information from anupstream station (e.g., a BS 110 a or a UE 120 r) and sends atransmission of the data and/or other information to a downstreamstation (e.g., a UE 120 or a BS 110), or that relays transmissionsbetween UEs 120, to facilitate communication between devices.

A network controller 130 may couple to a set of BSs 110 and providecoordination and control for these BSs 110. The network controller 130may communicate with the BSs 110 via a backhaul. The BSs 110 may alsocommunicate with one another (e.g., directly or indirectly) via wirelessor wireline backhaul.

FIG. 2 illustrates example components of BS 110 a and UE 120 a (e.g., inthe wireless communication network 100 of FIG. 1), which may be used toimplement aspects of the present disclosure.

At the BS 110 a, a transmit processor 220 may receive data from a datasource 212 and control information from a controller/processor 240. Thecontrol information may be for the physical broadcast channel (PBCH),physical control format indicator channel (PCFICH), physical hybrid ARQindicator channel (PHICH), physical downlink control channel (PDCCH),group common PDCCH (GC PDCCH), etc. The data may be for the physicaldownlink shared channel (PDSCH), etc. The processor 220 may process(e.g., encode and symbol map) the data and control information to obtaindata symbols and control symbols, respectively. The transmit processor220 may also generate reference symbols, such as for the primarysynchronization signal (PSS), secondary synchronization signal (SSS),and cell-specific reference signal (CRS). A transmit (TX) multiple-inputmultiple-output (MIMO) processor 230 may perform spatial processing(e.g., precoding) on the data symbols, the control symbols, and/or thereference symbols, if applicable, and may provide output symbol streamsto the modulators (MODs) 232 a-232 t. Each modulator 232 may process arespective output symbol stream (e.g., for OFDM, etc.) to obtain anoutput sample stream. Each modulator may further process (e.g., convertto analog, amplify, filter, and upconvert) the output sample stream toobtain a downlink signal. Downlink signals from modulators 232 a-232 tmay be transmitted via the antennas 234 a-234 t, respectively.

At the UE 120 a, the antennas 252 a-252 r may receive the downlinksignals from the BS 110 a and may provide received signals to thedemodulators (DEMODs) in transceivers 254 a-254 r, respectively. Eachdemodulator 254 may condition (e.g., filter, amplify, downconvert, anddigitize) a respective received signal to obtain input samples. Eachdemodulator may further process the input samples (e.g., for OFDM, etc.)to obtain received symbols. A MIMO detector 256 may obtain receivedsymbols from all the demodulators 254 a-254 r, perform MIMO detection onthe received symbols if applicable, and provide detected symbols. Areceive processor 258 may process (e.g., demodulate, deinterleave, anddecode) the detected symbols, provide decoded data for the UE 120 a to adata sink 260, and provide decoded control information to acontroller/processor 280.

On the uplink, at UE 120 a, a transmit processor 264 may receive andprocess data (e.g., for the physical uplink shared channel (PUSCH)) froma data source 262 and control information (e.g., for the physical uplinkcontrol channel (PUCCH) from the controller/processor 280. The transmitprocessor 264 may also generate reference symbols for a reference signal(e.g., for the sounding reference signal (SRS)). The symbols from thetransmit processor 264 may be precoded by a TX MIMO processor 266 ifapplicable, further processed by the demodulators in transceivers 254a-254 r (e.g., for SC-FDM, etc.), and transmitted to the BS 110 a. Atthe BS 110 a, the uplink signals from the UE 120 a may be received bythe antennas 234, processed by the modulators 232, detected by a MIMOdetector 236 if applicable, and further processed by a receive processor238 to obtain decoded data and control information sent by the UE 120 a.The receive processor 238 may provide the decoded data to a data sink239 and the decoded control information to the controller/processor 240.

The memories 242 and 282 may store data and program codes for BS 110 aand UE 120 a, respectively. A scheduler 244 may schedule UEs for datatransmission on the downlink and/or uplink.

The controller/processor 280 and/or other processors and modules at theUE 120 a may perform or direct the execution of processes for thetechniques described herein for handling a radio link failure timer inthe presence of a conditional handover command. For example, as shown inFIG. 2, the controller/processor 280 of the UE 120 a includes an RLFmanager 281 that may be configured for performing the operationsillustrated in one or more of FIGS. 4-7 as well as other operationsdescribed herein for handling a radio link failure timer in the presenceof a conditional handover command, according to aspects describedherein. Although shown at the Controller/Processor, other components ofthe UE 120 a and BS 110 a may be used performing the operationsdescribed herein.

Example Early Radio Link Failure Detection

In certain cases, a radio link between a UE 120 and a base station 110may deteriorate to the point that effective communication between the UE120 and the base station 110 are terminated. In this case, the basestation may drop context information for the UE and the UE may perform aradio link failure (RLF) procedure. The RLF procedure may involveestablishing a new radio connection with a neighboring base station. Thenew neighboring base station may attempt to obtain the contextinformation from the previous serving station. However, if the previousbase station has dropped the context information, the neighboring basestation's request may fail and a delay may be incurred while the newbase station and the UE reestablish a new context. Thus, to avoid suchdelay, an early RLF detection mechanism has been introduced to allow aUE to detect that an RLF is imminent and handover to the neighboringbase station before the RLF occurs.

FIG. 3 illustrates an example of a decision flow 300 for early RLFdeclaration in accordance with aspects of the present disclosure.Decision flow 300 may represent steps performed by a UE 120 as describedwith reference to FIGS. 1-2.

At step 305, a UE 120 may monitor the channel conditions of a servingcell and one or more neighbor cells. For example, the UE 120 may receivea measurement configuration from a base station 110 as part of an RRCconfiguration message indicating a set of neighbor cells to monitor.During the monitoring, the UE 120 may measure values of the serving celland one or more cells from the set of neighbor cells, the valuescorresponding to one or more channel parameters of the cells.

At step 310, the UE may identify a measurement reporting trigger, suchas an measurement report message (MRM) trigger event that has occurredor been triggered. In some examples, the measurement reporting triggeris an A1, A2, A3, A4, A5, B1, or B2 event in a measurement configurationof the UE.

For example, in some cases, a first measurement reporting trigger (e.g.,A1) may occur when the serving cell becomes better than a threshold; asecond measurement reporting trigger (e.g., A2) may occur when theserving cell becomes worse than a threshold; a third measurementreporting trigger (e.g., A3) may occur when a neighbor cell becomesbetter than the primary serving cell by an offset value; a secondmeasurement reporting trigger (e.g., A4) may occur when a neighbor cellbecomes better than a threshold; a fifth measurement reporting trigger(e.g., A5) may occur when the primary serving cell becomes worse than athreshold and a neighbor cell is simultaneously better than another(e.g., higher) threshold; a sixth measurement reporting trigger (e.g.,A6) may occur when a neighbor cell becomes better than a secondaryserving cell by an offset value; a seventh measurement reporting trigger(e.g., B1) may occur when a neighbor using a different radio accesstechnology (RAT) becomes better than a threshold; and an eighthmeasurement reporting trigger (e.g., B2) may occur when a primaryserving cell becomes worse than a threshold and the inter-RAT neighborbecomes better than another threshold.

In some examples, if the UE 120 identifies a measurement report trigger,at step 315 the UE 120 may initiate a first RLF timer (e.g., a T310timer) based on an MRM trigger.

At step 316, the UE 120 may transmit an UL message, such as an MRM orother UL radio link signaling message, based on the MRM trigger. The RLFtimer may be used in conjunction with, or independent, of other timersused for declaration of RLF. For example, in some cases, a T310 timermay be triggered based on detection of a PHY layer problem at theserving cell (e.g., when a number of out-of-sync indications reaches athreshold). A T312 timer may be another example of a timer that may beused in conjunction with the RLF timer. For example, the T312 timer maybe started/triggered when T310 is running and an MRM is sent to theserving cell based on a measurement report trigger/identity for which aT312 has been configured (e.g., A1, A2, A3, A4, A5, B1, or B2 eventidentities). In some cases, since the T310 timer may be relatively long,the T312 timer may be used to facilitate faster RLF recovery, forexample, by allowing earlier expiry of the T310 timer.

At step 330, the UE 120 may detect whether a radio link conditionindicative of an RLF has been satisfied, the determination prompted bythe identified measurement reporting trigger. For example, thisdetermination may be based on a determination of whether an RLC layerACK for the UL message has been received, such as an RLC layer ACK inresponse to one or more MRMs or other UL radio link signaling messages.In various examples, if an RLC layer ACK is not received, it may be anindication that channel conditions for the serving cell havedeteriorated significantly.

Even if an RLC layer ACK is received—or in some cases if the RLC layerACK is not received—the UE 120 may otherwise determine that RLF isimminent. For example, at step 330, the UE 120 may wait for a handovercommand based on the UL radio link signaling message transmission. Insome cases, even though an RLC layer ACK is received by the UE 120(confirming that the serving cell received the MRM), the UE 12 may notreceive an ensuing handover command based on a low channel quality forthe serving cell.

If the handover command is received, at step 335 the UE 115 may stop theT312 timer and perform the handover as directed. Additionally, the T312timer may be stopped based on other criteria, such as upon receivingN311 consecutive in-sync indications, upon initiating a connectionre-establishment procedure, or expiration of the T310 timer.

If, however, a handover command is not received at step 335, the UE 120may, at step 340, determine that the RLF timer has expired. This lack ofa handover command and the expiration of the RLF timer may satisfy aradio link condition indicative of an RLF.

As an additional or alternative method of determining that RLF isimminent, if at step 320 the RLC layer ACK for the UL message, such asan RLC layer ACK in response to an MRM message or other UL radio linksignaling message, is not received, the UE 120 may increment a counterand then determine whether the counter for the number of RLC layer ACKsexceeds a threshold. If the threshold is not exceeded, the UE 120 mayretransmit the UL message at step 316 and wait for another RLC layerACK. But at step 325 if the number of UL messages transmitted withoutRLC layer ACK exceeds the threshold, the UE 120 may determine that theradio link condition for imminent RLF is satisfied. In some examples,the radio link condition may be further based on a traffic typeindication. For example, the length of the RLF timer or other aspects ofthe radio link condition process may depend on whether the traffic typeis a VoLTE traffic type (or another traffic type with a QoS standard).

Some examples may include step 345, where once the UE 120 has detectedthe condition indicative of a RLF (e.g., based on the RLF timer or theRLC layer ACK threshold); the UE 120 may optionally verify that achannel comparison condition has been satisfied based on a serving cellchannel parameter and a target cell channel parameter. In some examples,verifying that the channel comparison condition has been satisfiedincludes: determining that the serving cell channel parameter is below afirst threshold and determining that the target cell channel parameteris above a second threshold. In some examples, verifying that thechannel comparison condition has been satisfied includes: determiningthat the target cell channel parameter exceeds the serving cell channelparameter by an offset value. The verification of the channel comparisoncondition may serve to ensure that channel conditions have not recoveredat the serving cell or deteriorated at the target cell during theprocess of determining that RLF is imminent.

At step 350, if the UE 120 has detected a condition indicative of RLF,and in some examples if the channel comparison condition is alsosatisfied, the UE 120 may initiate an RLF procedure based at least inpart on the detected condition indicative of RLF, and where applicablebased on the verification that the channel comparison condition has beensatisfied. For example, at step 350 the UE may declare an RLF. In someexamples the UE 120 may then initiate a connection re-establishmentprocedure to establish a connection to the target cell after initiatingthe RLF procedure, such as after a declared RLF. In some cases, this maybe an early RLF declaration that may mitigate any service disruptionassociated with the transition to the new cell. For example, it mayenable the target cell to retrieve context for the UE 120 before theserving cell drops the context.

Conditional Handover and Radio Link Failure Timer Interaction

As noted above, a UE may use one or more timers for radio link failure(RLF) detection and recovery. Such timers may include the T310 timer andthe T312 timer. For example, in some cases, the UE may be communicatewith a serving cell via a communication link. In certain cases, the UEmay trigger the T310 timer based on detection of a PHY layer problem atthe serving cell (e.g., the communication link is deteriorating), suchas receiving a number of out-of-sync indications reaches a threshold. Insome cases, the UE may receive configuration information for one or moremeasurement objects that include an indication of one or moremeasurement event triggers configured for the serving cell.Additionally, a timer, such as the T312 timer, may be configured for theone or more measurement event triggers in the one or more measurementobjects.

According to aspects, the UE may perform monitoring for the one or moremeasurement event triggers in the one or more measurement objects and,upon detecting one or more of the measurement event triggers and if theT310 timer is already running, the UE may trigger the T312 timer for ameasurement event for which T312 has been configured. In some cases, theUE may detect the one or more event triggers based on measurementsperformed on one or more signals from the serving cell. Upon detectingthe one or more measurement event triggers, the UE may transmit ameasurement report. In some cases, the one or more signals may includeone or more reference signals, such as one or more channel stateinformation reference signals (CSI-RSs) and/or one or moresynchronization signal blocks (SSBs).

According to aspects, the T312 timer may be used to facilitate fasterRLF recovery by allowing for early termination of the T310 timer. Forexample, in certain cases, if the UE fails to receive a response to thetransmitted measurement report before expiration of the T312 timer, theUE may declare an RLF and stop the T310 timer. Thereafter, afterexpiration of the T312 timer, the UE may take one or more actions, suchas transitioning to a radio resource control (RRC) idle mode orinitiating a connection re-establishment procedure to connect to aneighboring cell.

In some cases, the UE may stop the T312 timer before it expires. Forexample, the UE may determine to stop the T312 timer before it expireswhen (1) the UE receives N311 consecutive in-sync indications from lowerlayers, (2) the UE receives a handover command triggering a handoverprocedure to a neighbor cell, (3) when a connection re-establishmentprocedure is initiated, or (4) upon expiry of the T310 timer.

According to aspects, the RLF timers discussed above have traditionallybeen associated with normal handovers. However, more recently, theconcept of a conditional handover has been introduced. A conditionalhandover is a type of handover in which the serving cell provides the UEwith a handover command that includes one or more triggering conditionsfor autonomously initiating a handover to a candidate neighbor cell. Forexample, upon receiving a conditional handover command, the UE may beginto monitor one or more candidate neighbor cells. If the UE detects thatthe one or more triggering conditions have been satisfied with respectto a candidate neighbor cell, the UE may autonomously initiate ahandover to that neighbor cell without further assistance from theserving cell.

However, it is currently unspecified how conditional handovers shouldinteract with the RLF timers discussed above. Thus, aspects of thepresent disclosure provide techniques for handling an RLF timer (e.g.,starting, stopping, expiry behavior) in the presence of a conditionalhandover command. In some cases, techniques for handling an RLF timer inthe presence of a conditional handover may depend, for example, onwhether the UE has already been configured with a conditional handoverupon triggering of the RLF timer. Thus, aspects of the presentdisclosure provide techniques for handling the case where no conditionalhandover configuration is active in the UE before triggering of the RLFtimer. Additionally, aspects of the present disclosure providetechniques for handling the case where there is a conditional handoverconfiguration active in the UE before the triggering of the RLF timer.

For example, in some cases, an RLF timer, such as a T312 timer, may bestarted similar to LTE legacy behavior (e.g., upon triggering ameasurement report for a measurement identity for which the T312 timerhas been configured, while the T310 timer is running) even when themeasurement report is triggered for configuring a conditional handover(e.g., for providing the serving cell with information to configure theconditional handover). Additionally, in some cases, the RLF timer may bestarted even when a conditional handover has already been configured atthe UE and before the conditional handover is executed by the UE, forexample, while UE is monitoring the target neighbor cells identified bythe conditional handover. According to aspects, in this case, ameasurement report may be triggered on the source cell for a measurementidentity for which the T312 timer has been configured, while the T310timer is running.

According to aspects, the RLF timer may be stopped in certain cases. Forexample, in some cases the UE may stop the RLF timer upon receiving aconditional handover radio resource control (RRC) reconfigurationmessage. Additionally, in some cases, the RLF timer may be stopped uponexecution of the conditional handover command to hand the UE over to acandidate neighbor cell, for example, if the UE is configured by theconditional handover command to monitor for one or more triggeringconditions corresponding to the candidate neighbor cell prior to thestart of RLF timer.

In some cases, the RLF timer may become expired. According to aspects,in this case, upon expiration of the RLF timer, even when theconditional handover is configured but not executed, the UE may followlegacy LTE T312 timer expiry behavior. For example, if the RLF timerexpires and if security is not activated, the UE may take one or moreactions, such as entering an idle mode (e.g., RRC_IDLE) or may initiatea connection re-establishment procedure to establish a communicationlink with a candidate neighbor cell.

FIG. 4 is a flow diagram illustrating example operations 400 forwireless communication, in accordance with certain aspects of thepresent disclosure. The operations 400 may be performed, for example, byUE (e.g., such as a UE 120 a in the wireless communication network 100)for handling the case where no conditional handover configuration isactive in the UE before triggering of the RLF timer. Operations 400 maybe implemented as software components that are executed and run on oneor more processors (e.g., controller/processor 280 of FIG. 2). Further,the transmission and reception of signals by the UE in operations 400may be enabled, for example, by one or more antennas (e.g., antennas 252of FIG. 2). In certain aspects, the transmission and/or reception ofsignals by the UE may be implemented via a bus interface of one or moreprocessors (e.g., controller/processor 280) obtaining and/or outputtingsignals.

The operations 400 may begin, at 405, by communicating with a servingcell over a communication link.

At 410, the UE monitors at least one of one or more signals from theserving cell or one or more signals from one or more candidate neighborcells based, at least in part, on one or more measurement eventsconfigured in one or more measurement objects. For example, in somecases, the UE may receive configuration information that includes one ormore measurement objects, indicating the one or more measurement eventsor measurement event triggers. In some cases, the one or moremeasurement events may include, for example, one or more of the A1, A2,A3, A4, A5, B1, or B2 event identities discussed above. Additionally, insome cases, the one or more measurement objects may be configured, bythe serving cell, for reporting the one or more candidate neighbor cellsfor at least one of normal handover (HO), make-before-break HO, randomaccess channel (RACH)-less HO, or conditional HO.

At 415 the UE detects the one or more measurement events based on themonitoring, wherein a timer is configured for the one or moremeasurement events in the one or more measurement objects. In somecases, the timer may be a T312 timer, as discussed above.

At 420, the UE starts the timer based on detecting the one or moremeasurement events. In some cases, the UE may start the timer whenanother timer, such as a T310, timer is already running. For example, asnoted above, the UE may have previously started the T310 timer inresponse to detecting that a signal quality associated with thecommunication link is deteriorating.

At 425, the UE transmits a measurement report based on the detected oneor more measurement events. In some cases, the measurement report mayinclude parameters indicating a channel/signal quality associated withthe serving cell (e.g., the communication link) and the one or morecandidate neighbor cells.

At 430, the UE receives a conditional handover command for handing theUE over to a candidate target cell of the one or more candidate neighborcells. In some cases, the conditional handover command includes one ormore triggering conditions for executing a conditional handover to thecandidate neighbor cell.

At 435, the UE stops the timer based on the received conditionalhandover command.

Additionally, in some cases, stopping the timer may further comprisereceiving an indication of a threshold number of in-sync indications.According to aspects, the UE may then stop the timer based on thereceived indication of a threshold number of in-sync indications.

Additionally, in some cases, stopping the timer may further compriseinitiating a handover procedure to hand the UE over to the candidatetarget cell. In some cases, initiating the handover procedure may bebased on a handover command instructing the UE to handover to thecandidate target cell. In response, the UE may stop the timer based onthe initiated handover procedure.

Additionally, in some cases, stopping the timer may further compriseinitiating a connection re-establishment procedure to re-establish thecommunication link. According to aspects, in response, the UE may stopthe timer based on the initiated connection re-establishment procedure.

Additionally, in some cases, stopping the timer may comprise determiningthat a second timer is expired. In some cases, the second timer maycomprise a T310 timer. According to aspects, based on expiration of theT310 timer, the UE may stop the T312 timer.

FIG. 5 illustrates a call-flow diagram showing example operations forhandling the case where no conditional handover configuration is activein the UE before triggering of the RLF timer, according to certainaspects presented herein.

According to aspects, while not explicitly illustrated in FIG. 5, a UE502 may communicate with a serving cell 504 (e.g., source gNB) over acommunication link. In some cases, the UE 502 and serving cell 504 maycomprise the UE 120 and BS 110, respectively, discussed above. At somepoint in time, the UE 502 may detect that a signal quality associatedwith the communication link is deteriorating and may start a T310 timer,as illustrated at 520. According to aspects, after starting the T310timer at 520, the UE 502 may monitor at least one of one or more signalsfrom the serving cell 504 or one or more signals from one or morecandidate neighbor cells (e.g., candidate neighbor cell 506 andcandidate neighbor cell 508, also known as candidate target cells)based, at least in part, on one or more configured measurement events inone or more received measurement objects. Based on the monitoring, theUE 502 may detect one or more measurement events (e.g., one or moremeasurement event triggers) at 522. In some cases, a second timer, suchas a T312 timer, may be configured for the one or more measurementevents in the one or more measurement objects.

According to aspects, the UE may start the T312 timer at 524 andtransmit a measurement report at 526 based on detecting the one or moremeasurement events.

Thereafter, as shown at 528 and 529, based on the measurement report,the serving cell 504 may prepare a conditional handover command forhanding the UE over to a candidate target cell of the one or morecandidate neighbor cell, such as the candidate neighbor cell 506 orcandidate neighbor cell 508. In some cases, preparing the conditionalhandover command may include preparing the candidate target cell for thehandover, for example, by transmitting UE context information to thecandidate cell (e.g., as illustrated at 528 and 529). In some cases, theconditional handover command includes one or more triggering conditionsfor executing a conditional handover to the candidate neighbor cell.Additionally, in some cases, the conditional handover command mayinclude information for accessing the candidate target cell.

Thereafter, at 530, the serving cell 504 may transmit the conditionalhandover command to the UE 502. In some cases, the conditional handovercommand may be transmitted/received in an RRC reconfiguration message.

According, in response to receiving the conditional handover command,the UE may stop the T312 timer and the T310 timer at 532. Additionally,the UE may stop the T312 timer in other circumstances, such as (1)receiving an indication of a threshold number of in-sync indications,(2) receiving a handover command and initiating a handover procedure tohand the UE over to the candidate target cell, (3) initiating aconnection re-establishment procedure to re-establish the communicationlink, or (4) upon the expiration of the T310 timer.

According to aspects, the operations illustrated in FIG. 5 illustratethat the T312 timer may be started due to a measurement event triggerfor a measurement object configured for normal HO reporting orconditional handover cell reporting that have T312 configured. Accordingto aspects, the T312 timer may be reset if another measurement report istriggered for any of the T312 configured measurement objects while T312is running.

FIG. 6 is a flow diagram illustrating example operations 600 forwireless communication, in accordance with certain aspects of thepresent disclosure. The operations 600 may be performed, for example, byUE (e.g., such as a UE 120 a in the wireless communication network 100)for handling the case where there is conditional handover configurationactive in the UE before the triggering of the RLF timer. Operations 600may be implemented as software components that are executed and run onone or more processors (e.g., controller/processor 280 of FIG. 2).Further, the transmission and reception of signals by the UE inoperations 600 may be enabled, for example, by one or more antennas(e.g., antennas 252 of FIG. 2). In certain aspects, the transmissionand/or reception of signals by the UE may be implemented via a businterface of one or more processors (e.g., controller/processor 280)obtaining and/or outputting signals.

The operations 600 may begin, at 605, by receiving, from a serving cell,a conditional handover command for handing over the UE to a targetneighbor cell, wherein the conditional handover command includes one ormore triggering conditions for executing a handover to a candidateneighbor cell.

At 610, the UE monitors one or more first signals from the candidatetarget cell for the one or more triggering conditions.

At 615, the UE performs one of stopping a timer based on performing aconditional handover to the target candidate cell or detecting a timerhas expired while monitoring the one or more first signals from thecandidate target cell for the one or more triggering conditions. In somecases, the timer may comprise a T312 timer.

For example, in some cases, stopping the timer may include detectingthat at least one of the one or more triggering conditions are satisfiedbased on the monitored one or more first signals. Thereafter, the UE mayperforming a conditional handover to the candidate target cell based ondetecting that at least one of the one or more triggering conditions aresatisfied. According to aspects, the UE may then stop the timer based onperforming the conditional handover to the candidate target cell.

According to aspects, if the UE detects that the timer has expired whilemonitoring the one or more first signals from the candidate target cellfor the one or more triggering conditions, the UE may take one or moreactions. For example, in some cases, as the one or more action maycomprise at least one of transitioning into an idle mode of operation(e.g., RRC_IDLE) or initiating a connection re-establishment procedureto one or more neighbor cells, such as the candidate target cell.

In some cases, operations 600 may further include detecting one or moremeasurement events based on monitoring for one or more measurementobjects configured for the serving cell. In this case, the timer may beconfigured for the one or more measurement events in the one or moremeasurement objects. Additionally, in this case, starting the timer maycomprise starting the timer after detecting the one or more measurementevents but before detecting that the one or more triggering conditionsare satisfied. Additionally, in some cases, operations 600 may furtherinclude transmitting a measurement report based on the detected one ormore measurement events. In some cases, the measurement report mayinclude parameters indicating a channel/signal quality associated withthe serving cell (e.g., the communication link) and the one or morecandidate neighbor cells.

As noted above, the UE may stop the timer when the conditional handoverto the candidate target cell is executed. The UE may also stop the timerin other circumstances. For example, in some cases, stopping the timermay further comprise receiving an indication of a threshold number ofin-sync indications. According to aspects, the UE may then stop thetimer based on the received indication of a threshold number of in-syncindications.

Additionally, in some cases, stopping the timer may further compriseinitiating a handover procedure to hand the UE over to the candidatetarget cell. In some cases, initiating the handover procedure is basedon a handover command instructing the UE to handover to the candidatetarget cell. In response, the UE may stop the timer based on theinitiated handover procedure.

Additionally, in some cases, stopping the timer may further compriseinitiating a connection re-establishment procedure to re-establish thecommunication link. According to aspects, in response, the UE may stopthe timer based on the initiated connection re-establishment procedure.

Additionally, in some cases, stopping the timer may comprise determiningthat a second timer is expired. In some cases, the second timer maycomprise a T310 timer. According to aspects, based on expiration of theT310 timer, the UE may stop the T312 timer.

Additionally, in some cases, stopping the timer may comprise receiving asecond conditional handover command to configure the UE with one or moreother candidate target cells. In response, the UE may stop the timerbased on the received second conditional handover command.

FIG. 7 illustrates a call-flow diagram showing example operations forhandling the case where conditional handover configuration is active inthe UE before triggering of the RLF timer, according to certain aspectspresented herein.

As illustrated, the UE 702 may detect one or more measurement events at720 and transmit a measurement report at 722 to the serving cell 704(e.g., source gNB) via a communication link between the UE 702 and theserving cell 704. In some cases, the UE 702 and serving cell 704 maycomprise the UE 120 and BS 110, respectively, discussed above.

According to aspects, at 724 and 725, the serving cell may prepare aconditional handover command for handing the UE over to a candidatetarget cell of the one or more candidate neighbor cells, such as thecandidate neighbor cell 706 (e.g., candidate target gNB1) or thecandidate neighbor cell 708 (e.g., candidate target gNB2). In somecases, the conditional handover command includes one or more triggeringconditions for executing a conditional handover to the candidate targetcell. Additionally, in some cases, the conditional handover command mayinclude information for accessing the candidate target cell. Thereafter,as illustrated at 726, the serving cell 704 may transmit the conditionalhandover command to the UE 702. In some cases, the conditional handovercommand may be transmitted/received in an RRC Reconfiguration message.

According to aspects, after receiving the conditional handover command,the UE 702 may start a T310 timer at 728 and at 730 begins monitoringone or more first signals from the candidate target cell for the one ormore one or more triggering conditions. In some cases, the UE 702 maystart the T310 timer at 728 and begin monitoring the one or more firstsignals from the candidate target cell at 730 based on a detection thata signal quality associated with the communication link between the UE702 and serving cell 704 is deteriorating.

According to aspects, during monitoring of the one or more first signalsfrom the candidate target cell, the UE 702 may detect one or moremeasurement events at 732 based on monitoring for one or moremeasurement objects configured for the serving cell. In some cases, atimer, such as a T312 timer, may be configured for the one or moremeasurement events in the one or more measurement objects. According toaspects, the UE 702 may then start the timer at 734 based on detectingthe one or more measurement events. According to aspects, in some cases,starting the timer may comprise starting the timer after detecting theone or more measurement events but before detecting that the one or moretriggering conditions for executing a conditional handover to thecandidate target cell are satisfied.

In some cases, the UE 702 may start the timer when another timer, suchas a T310, timer is already running, as shown. As noted above, the UE702 may have previously started the T310 timer at 728 in response todetecting that a signal quality associated with the communication linkbetween the UE 702 and serving cell 704 is deteriorating.

According to aspects, after detecting the one or more measurementevents, the UE 702 may transmit at 736 a measurement report to theserving cell 704. In some cases, based on the measurement report, theserving cell 704 may cancel the conditional handover to the candidatetarget cell (e.g., the candidate target cell 706) as shown at 738 andtransmit a second conditional handover command with one or more othercandidate target cells as shown at 740. According to aspects, uponreceiving the second conditional handover command, the UE 702 may stopthe T312 timer and T310 timer at 742.

In some cases, while not illustrated in FIG. 7, the UE 702 may detectthat at least one of the one or more triggering conditions received inthe (first) conditional handover command are satisfied based on themonitored one or more first signals from the candidate target cell. Inthis case, the UE 702 may execute/perform a conditional handover to thecandidate target cell based on detecting that at least one of the one ormore triggering conditions are satisfied. Further, the UE 702 may stopthe T312 timer based on performing the conditional handover to thecandidate target cell.

In some cases, while not illustrated in FIG. 7, the UE 702 may detectthat the timer (e.g., T312 timer) has expired while monitoring the oneor more first signals from the candidate target cell for the one or moretriggering conditions. In this case, the UE 702 may take one or moreactions, such as transitioning into an idle mode of operation (e.g.,RRC_IDLE) or initiating a connection re-establishment procedure to oneor more neighbor cells, such as the candidate target cell.

According to aspects the operations illustrated in FIG. 7 illustratethat the UE may already be configured with a conditional handoverreceived via RRC message and is monitoring the one or more triggeringconditions received in the conditional handover command. According toaspects, the T312 timer may be started due to one or more measurementevent triggers for a measurement object configured for normal HOreporting or conditional handover cell reporting that have T312configured, for example, while UE is monitoring the trigger conditions.

FIG. 8 illustrates a communications device 800 that may include variouscomponents (e.g., corresponding to means-plus-function components)configured to perform operations for the techniques disclosed herein,such as the operations illustrated in FIGS. 4-5. The communicationsdevice 800 includes a processing system 802 coupled to a transceiver808. The transceiver 808 is configured to transmit and receive signalsfor the communications device 800 via an antenna 810, such as thevarious signals as described herein. The processing system 802 may beconfigured to perform processing functions for the communications device800, including processing signals received and/or to be transmitted bythe communications device 800.

The processing system 802 includes a processor 804 coupled to acomputer-readable medium/memory 812 via a bus 806. In certain aspects,the computer-readable medium/memory 812 is configured to storeinstructions (e.g., computer-executable code) that when executed by theprocessor 804, cause the processor 804 to perform the operationsillustrated in FIGS. 4-5, or other operations for performing the varioustechniques discussed herein for handling a radio link failure timer inthe presence of a conditional handover command. In certain aspects,computer-readable medium/memory 812 stores code for performing theoperations illustrated in one or more of FIGS. 4-5. For example,computer-readable medium/memory 812 stores code 814 for communicatingwith a serving cell over a communication link; code 816 for monitoringat least one of one or more signals from the serving cell or one or moresignals from one or more candidate neighbor cells based, at least inpart, on one or more measurement events configured in one or moremeasurement objects; code 818 for detecting the one or more measurementevents based on the monitoring, wherein a timer is configured for theone or more measurement events in the one or more measurement objects;code 820 for starting the timer based on detecting the one or moremeasurement events; code 822 for transmitting a measurement report basedon the detected one or more measurement events; code 824 for receiving aconditional handover command for handing the UE over to a candidatetarget cell of the one or more candidate neighbor cells, wherein theconditional handover command includes one or more triggering conditionsfor executing a conditional handover to the candidate target cell; andcode 826 for stopping the timer based on the received conditionalhandover command.

In certain aspects, the processor 804 may include circuitry configuredto implement the code stored in the computer-readable medium/memory 812,such as for performing the operations illustrated in FIGS. 4-5. Forexample, the processor 804 includes circuitry 828 for communicating witha serving cell over a communication link; circuitry 830 for monitoringat least one of one or more signals from the serving cell or one or moresignals from one or more candidate neighbor cells based, at least inpart, on one or more measurement events configured in one or moremeasurement objects; circuitry 832 for detecting the one or moremeasurement events based on the monitoring, wherein a timer isconfigured for the one or more measurement events in the one or moremeasurement objects; circuitry 834 for starting the timer based ondetecting the one or more measurement events; circuitry 836 fortransmitting a measurement report based on the detected one or moremeasurement events; circuitry 838 for receiving a conditional handovercommand for handing the UE over to a candidate target cell of the one ormore candidate neighbor cells, wherein the conditional handover commandincludes one or more triggering conditions for executing a conditionalhandover to the candidate target cell; and circuitry 840 for stoppingthe timer based on the received conditional handover command.

FIG. 9 illustrates a communications device 900 that may include variouscomponents (e.g., corresponding to means-plus-function components)configured to perform operations for the techniques disclosed herein,such as the operations illustrated in FIGS. 6-7. The communicationsdevice 900 includes a processing system 802 coupled to a transceiver908. The transceiver 908 is configured to transmit and receive signalsfor the communications device 900 via an antenna 910, such as thevarious signals as described herein. The processing system 902 may beconfigured to perform processing functions for the communications device900, including processing signals received and/or to be transmitted bythe communications device 900.

The processing system 902 includes a processor 904 coupled to acomputer-readable medium/memory 912 via a bus 906. In certain aspects,the computer-readable medium/memory 912 is configured to storeinstructions (e.g., computer-executable code) that when executed by theprocessor 904, cause the processor 904 to perform the operationsillustrated in FIGS. 6-7, or other operations for performing the varioustechniques discussed herein for handling a radio link failure timer inthe presence of a conditional handover command. In certain aspects,computer-readable medium/memory 912 stores code for performing theoperations illustrated in one or more of FIGS. 6-7. For example,computer-readable medium/memory 912 stores code 914 for receiving, froma serving cell, a conditional handover command for handing over the UEto a target neighbor cell, wherein the conditional handover commandincludes one or more triggering conditions for executing a handover to acandidate target cell; code 916 for monitoring; and code 918 forperforming one of stopping a timer based on performing a conditionalhandover to the target candidate cell or detecting a timer has expiredwhile monitoring the one or more first signals from the candidate targetcell for the one or more triggering conditions.

In certain aspects, the processor 904 may include circuitry configuredto implement the code stored in the computer-readable medium/memory8912, such as for performing the operations illustrated in FIGS. 6-7.For example, the processor 804 includes circuitry 920 for receiving,from a serving cell, a conditional handover command for handing over theUE to a target neighbor cell, wherein the conditional handover commandincludes one or more triggering conditions for executing a handover to acandidate target cell; circuitry 922 for monitoring; and circuitry 924for performing one of stopping a timer based on performing a conditionalhandover to the target candidate cell or detecting a timer has expiredwhile monitoring the one or more first signals from the candidate targetcell for the one or more triggering conditions.

The techniques described herein may be used for various wirelesscommunication technologies, such as NR (e.g., 5G NR), 3GPP Long TermEvolution (LTE), LTE-Advanced (LTE-A), code division multiple access(CDMA), time division multiple access (TDMA), frequency divisionmultiple access (FDMA), orthogonal frequency division multiple access(OFDMA), single-carrier frequency division multiple access (SC-FDMA),time division synchronous code division multiple access (TD-SCDMA), andother networks. The terms “network” and “system” are often usedinterchangeably. A CDMA network may implement a radio technology such asUniversal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. cdma2000 coversIS-2000, IS-95 and IS-856 standards. A TDMA network may implement aradio technology such as Global System for Mobile Communications (GSM).An OFDMA network may implement a radio technology such as NR (e.g. 5GRA), Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, etc. UTRA andE-UTRA are part of Universal Mobile Telecommunication System (UMTS). LTEand LTE-A are releases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE,LTE-A and GSM are described in documents from an organization named “3rdGeneration Partnership Project” (3GPP). cdma2000 and UMB are describedin documents from an organization named “3rd Generation PartnershipProject 2” (3GPP2). NR is an emerging wireless communications technologyunder development.

The techniques described herein may be used for the wireless networksand radio technologies mentioned above as well as other wirelessnetworks and radio technologies. For clarity, while aspects may bedescribed herein using terminology commonly associated with 3G, 4G,and/or 5G wireless technologies, aspects of the present disclosure canbe applied in other generation-based communication systems.

In 3GPP, the term “cell” can refer to a coverage area of a Node B (NB)and/or a NB subsystem serving this coverage area, depending on thecontext in which the term is used. In NR systems, the term “cell” andBS, next generation NodeB (gNB or gNodeB), access point (AP),distributed unit (DU), carrier, or transmission reception point (TRP)may be used interchangeably. A BS may provide communication coverage fora macro cell, a pico cell, a femto cell, and/or other types of cells. Amacro cell may cover a relatively large geographic area (e.g., severalkilometers in radius) and may allow unrestricted access by UEs withservice subscription. A pico cell may cover a relatively smallgeographic area and may allow unrestricted access by UEs with servicesubscription. A femto cell may cover a relatively small geographic area(e.g., a home) and may allow restricted access by UEs having anassociation with the femto cell (e.g., UEs in a Closed Subscriber Group(CSG), UEs for users in the home, etc.). A BS for a macro cell may bereferred to as a macro BS. A BS for a pico cell may be referred to as apico BS. ABS for a femto cell may be referred to as a femto BS or a homeBS.

A UE may also be referred to as a mobile station, a terminal, an accessterminal, a subscriber unit, a station, a Customer Premises Equipment(CPE), a cellular phone, a smart phone, a personal digital assistant(PDA), a wireless modem, a wireless communication device, a handhelddevice, a laptop computer, a cordless phone, a wireless local loop (WLL)station, a tablet computer, a camera, a gaming device, a netbook, asmartbook, an ultrabook, an appliance, a medical device or medicalequipment, a biometric sensor/device, a wearable device such as a smartwatch, smart clothing, smart glasses, a smart wrist band, smart jewelry(e.g., a smart ring, a smart bracelet, etc.), an entertainment device(e.g., a music device, a video device, a satellite radio, etc.), avehicular component or sensor, a smart meter/sensor, industrialmanufacturing equipment, a global positioning system device, or anyother suitable device that is configured to communicate via a wirelessor wired medium. Some UEs may be considered machine-type communication(MTC) devices or evolved MTC (eMTC) devices. MTC and eMTC UEs include,for example, robots, drones, remote devices, sensors, meters, monitors,location tags, etc., that may communicate with a BS, another device(e.g., remote device), or some other entity. A wireless node mayprovide, for example, connectivity for or to a network (e.g., a widearea network such as Internet or a cellular network) via a wired orwireless communication link. Some UEs may be consideredInternet-of-Things (IoT) devices, which may be narrowband IoT (NB-IoT)devices.

Certain wireless networks (e.g., LTE) utilize orthogonal frequencydivision multiplexing (OFDM) on the downlink and single-carrierfrequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDMpartition the system bandwidth into multiple (K) orthogonal subcarriers,which are also commonly referred to as tones, bins, etc. Each subcarriermay be modulated with data. In general, modulation symbols are sent inthe frequency domain with OFDM and in the time domain with SC-FDM. Thespacing between adjacent subcarriers may be fixed, and the total numberof subcarriers (K) may be dependent on the system bandwidth. Forexample, the spacing of the subcarriers may be 15 kHz and the minimumresource allocation (called a “resource block” (RB)) may be 12subcarriers (or 180 kHz). Consequently, the nominal Fast FourierTransfer (FFT) size may be equal to 128, 256, 512, 1024 or 2048 forsystem bandwidth of 1.25, 2.5, 5, 10, or 20 megahertz (MHz),respectively. The system bandwidth may also be partitioned intosubbands. For example, a subband may cover 1.08 MHz (e.g., 6 RBs), andthere may be 1, 2, 4, 8, or 16 subbands for system bandwidth of 1.25,2.5, 5, 10 or 20 MHz, respectively. In LTE, the basic transmission timeinterval (TTI) or packet duration is the 1 ms subframe.

NR may utilize OFDM with a CP on the uplink and downlink and includesupport for half-duplex operation using TDD. In NR, a subframe is still1 ms, but the basic TTI is referred to as a slot. A subframe contains avariable number of slots (e.g., 1, 2, 4, 8, 16, . . . slots) dependingon the subcarrier spacing. The NR RB is 12 consecutive frequencysubcarriers. NR may support a base subcarrier spacing of 15 KHz andother subcarrier spacing may be defined with respect to the basesubcarrier spacing, for example, 30 kHz, 60 kHz, 120 kHz, 240 kHz, etc.The symbol and slot lengths scale with the subcarrier spacing. The CPlength also depends on the subcarrier spacing. Beamforming may besupported and beam direction may be dynamically configured. MIMOtransmissions with precoding may also be supported. In some examples,MIMO configurations in the DL may support up to 8 transmit antennas withmulti-layer DL transmissions up to 8 streams and up to 2 streams per UE.In some examples, multi-layer transmissions with up to 2 streams per UEmay be supported. Aggregation of multiple cells may be supported with upto 8 serving cells.

In some examples, access to the air interface may be scheduled. Ascheduling entity (e.g., a BS) allocates resources for communicationamong some or all devices and equipment within its service area or cell.The scheduling entity may be responsible for scheduling, assigning,reconfiguring, and releasing resources for one or more subordinateentities. That is, for scheduled communication, subordinate entitiesutilize resources allocated by the scheduling entity. Base stations arenot the only entities that may function as a scheduling entity. In someexamples, a UE may function as a scheduling entity and may scheduleresources for one or more subordinate entities (e.g., one or more otherUEs), and the other UEs may utilize the resources scheduled by the UEfor wireless communication. In some examples, a UE may function as ascheduling entity in a peer-to-peer (P2P) network, and/or in a meshnetwork. In a mesh network example, UEs may communicate directly withone another in addition to communicating with a scheduling entity.

In some examples, two or more subordinate entities (e.g., UEs) maycommunicate with each other using sidelink signals. Real-worldapplications of such sidelink communications may include public safety,proximity services, UE-to-network relaying, vehicle-to-vehicle (V2V)communications, Internet of Everything (IoE) communications, IoTcommunications, mission-critical mesh, and/or various other suitableapplications. Generally, a sidelink signal may refer to a signalcommunicated from one subordinate entity (e.g., UE1) to anothersubordinate entity (e.g., UE2) without relaying that communicationthrough the scheduling entity (e.g., UE or BS), even though thescheduling entity may be utilized for scheduling and/or controlpurposes. In some examples, the sidelink signals may be communicatedusing a licensed spectrum (unlike wireless local area networks, whichtypically use an unlicensed spectrum).

The methods disclosed herein comprise one or more steps or actions forachieving the methods. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover a, b, c,a-b, a-c, b-c, and a-b-c, as well as any combination with multiples ofthe same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b,b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language of the claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. All structural andfunctional equivalents to the elements of the various aspects describedthroughout this disclosure that are known or later come to be known tothose of ordinary skill in the art are expressly incorporated herein byreference and are intended to be encompassed by the claims. Moreover,nothing disclosed herein is intended to be dedicated to the publicregardless of whether such disclosure is explicitly recited in theclaims. No claim element is to be construed under the provisions of 35U.S.C. § 112(f) unless the element is expressly recited using the phrase“means for” or, in the case of a method claim, the element is recitedusing the phrase “step for.”

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrated circuit (ASIC), or processor. Generally,where there are operations illustrated in figures, those operations mayhave corresponding counterpart means-plus-function components withsimilar numbering.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or other programmable logic device (PLD),discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

If implemented in hardware, an example hardware configuration maycomprise a processing system in a wireless node. The processing systemmay be implemented with a bus architecture. The bus may include anynumber of interconnecting buses and bridges depending on the specificapplication of the processing system and the overall design constraints.The bus may link together various circuits including a processor,machine-readable media, and a bus interface. The bus interface may beused to connect a network adapter, among other things, to the processingsystem via the bus. The network adapter may be used to implement thesignal processing functions of the PHY layer. In the case of a userterminal 120 (see FIG. 1), a user interface (e.g., keypad, display,mouse, joystick, etc.) may also be connected to the bus. The bus mayalso link various other circuits such as timing sources, peripherals,voltage regulators, power management circuits, and the like, which arewell known in the art, and therefore, will not be described any further.The processor may be implemented with one or more general-purpose and/orspecial-purpose processors. Examples include microprocessors,microcontrollers, DSP processors, and other circuitry that can executesoftware. Those skilled in the art will recognize how best to implementthe described functionality for the processing system depending on theparticular application and the overall design constraints imposed on theoverall system.

If implemented in software, the functions may be stored or transmittedover as one or more instructions or code on a computer readable medium.Software shall be construed broadly to mean instructions, data, or anycombination thereof, whether referred to as software, firmware,middleware, microcode, hardware description language, or otherwise.Computer-readable media include both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. The processor may beresponsible for managing the bus and general processing, including theexecution of software modules stored on the machine-readable storagemedia. A computer-readable storage medium may be coupled to a processorsuch that the processor can read information from, and write informationto, the storage medium. In the alternative, the storage medium may beintegral to the processor. By way of example, the machine-readable mediamay include a transmission line, a carrier wave modulated by data,and/or a computer readable storage medium with instructions storedthereon separate from the wireless node, all of which may be accessed bythe processor through the bus interface. Alternatively, or in addition,the machine-readable media, or any portion thereof, may be integratedinto the processor, such as the case may be with cache and/or generalregister files. Examples of machine-readable storage media may include,by way of example, RAM (Random Access Memory), flash memory, ROM (ReadOnly Memory), PROM (Programmable Read-Only Memory), EPROM (ErasableProgrammable Read-Only Memory), EEPROM (Electrically ErasableProgrammable Read-Only Memory), registers, magnetic disks, opticaldisks, hard drives, or any other suitable storage medium, or anycombination thereof. The machine-readable media may be embodied in acomputer-program product.

A software module may comprise a single instruction, or manyinstructions, and may be distributed over several different codesegments, among different programs, and across multiple storage media.The computer-readable media may comprise a number of software modules.The software modules include instructions that, when executed by anapparatus such as a processor, cause the processing system to performvarious functions. The software modules may include a transmissionmodule and a receiving module. Each software module may reside in asingle storage device or be distributed across multiple storage devices.By way of example, a software module may be loaded into RAM from a harddrive when a triggering event occurs. During execution of the softwaremodule, the processor may load some of the instructions into cache toincrease access speed. One or more cache lines may then be loaded into ageneral register file for execution by the processor. When referring tothe functionality of a software module below, it will be understood thatsuch functionality is implemented by the processor when executinginstructions from that software module.

Also, any connection is properly termed a computer-readable medium. Forexample, if the software is transmitted from a website, server, or otherremote source using a coaxial cable, fiber optic cable, twisted pair,digital subscriber line (DSL), or wireless technologies such as infrared(IR), radio, and microwave, then the coaxial cable, fiber optic cable,twisted pair, DSL, or wireless technologies such as infrared, radio, andmicrowave are included in the definition of medium. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers. Thus, in some aspects computer-readable media maycomprise non-transitory computer-readable media (e.g., tangible media).In addition, for other aspects computer-readable media may comprisetransitory computer-readable media (e.g., a signal). Combinations of theabove should also be included within the scope of computer-readablemedia.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer-readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein, for example, instructions for performing the operationsdescribed herein and illustrated in FIGS. 4-7.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

The invention claimed is:
 1. A method for wireless communication by auser equipment (UE), comprising: receiving, from a serving cell, aconditional handover command for handing over the UE to a targetneighbor cell, wherein the conditional handover command includes one ormore triggering conditions for executing a handover to a candidatetarget cell; detecting one or more measurement events in one or moremeasurement objects configured for the serving cell, wherein a timer isconfigured for the one or more measurement events in the one or moremeasurement objects; starting the timer based on the detection of theone or more measurement events in one or more measurement objectsconfigured for the serving cell; monitoring one or more first signalsfrom the candidate target cell for the one or more triggering conditionsbased on the detection of the one or more measurement events in one ormore measurement objects configured for the serving cell; and performingone of: stopping the timer based on performing a conditional handover tothe target candidate cell; or detecting a timer has expired whilemonitoring the one or more first signals from the candidate target cellfor the one or more triggering conditions.
 2. The method of claim 1,wherein starting the timer comprises starting the timer after detectingthe one or more measurement events but before detecting that the one ormore triggering conditions are satisfied.
 3. The method of claim 1,further comprising transmitting a measurement report based on thedetected one or more measurement events.
 4. The method of claim 1,wherein the timer comprises a T312 timer.
 5. The method of claim 1,wherein stopping the timer comprises: detecting that at least one of theone or more triggering conditions are satisfied based on the monitoredone or more first signals; performing a conditional handover to thecandidate target cell based on detecting that at least one of the one ormore triggering conditions are satisfied; and stopping the timer basedon performing the conditional handover to the candidate target cell. 6.The method of claim 1, further comprising taking one or more actionsbased on detecting that the timer has expired while monitoring the oneor more first signals from the candidate target cell for the one or moretriggering conditions.
 7. The method of claim 6, wherein taking one ormore actions comprises one of: transitioning into an idle mode ofoperation; or initiating a connection re-establishment procedure.
 8. Themethod of claim 1, wherein stopping the timer further comprises:receiving an indication of a threshold number of in-sync indications;and stopping the timer based on the received indication of a thresholdnumber of in-sync indications.
 9. The method of claim 1, whereinstopping the timer further comprises: initiating a handover procedure tohand the UE over to the target neighbor cell; and stopping the timerbased on the initiated handover procedure.
 10. The method of claim 9,wherein initiating the handover procedure is based on a handover commandinstructing the UE to handover to the target neighbor cell.
 11. Themethod of claim 1, wherein stopping the timer further comprises:receiving a second conditional handover command to configure the UE withone or more other candidate target cell; and stopping the timer based onthe received second conditional handover command.
 12. The method ofclaim 1, wherein stopping the timer further comprises: initiating aconnection re-establishment procedure to re-establish a communicationlink between the UE and the serving cell; and stopping the timer basedon the initiated connection re-establishment procedure.
 13. The methodof claim 1, wherein stopping the timer further comprises: determiningthat a second timer is expired; and stopping the timer based on theexpiration of the second timer.
 14. The method of claim 13, wherein thesecond timer comprises a T310 timer.
 15. An apparatus for wirelesscommunication by a user equipment (UE), comprising: at least oneprocessor configured to: receive, from a serving cell, a conditionalhandover command for handing over the UE to a target neighbor cell,wherein the conditional handover command includes one or more triggeringconditions for executing a handover to a candidate target cell; detectone or more measurement events in one or more measurement objectsconfigured for the serving cell, wherein a timer is configured for theone or more measurement events in the one or more measurement objects;start the timer based on the detection of the one or more measurementevents in one or more measurement objects configured for the servingcell; monitor one or more first signals from the candidate target cellfor the one or more triggering conditions based on the detection of theone or more measurement events in one or more measurement objectsconfigured for the serving cell; and perform one of: stopping a timerbased on performing a conditional handover to the target candidate cell;or detecting a timer has expired while monitoring the one or more firstsignals from the candidate target cell for the one or more triggeringconditions; and a memory coupled with the at least one processor. 16.The apparatus of claim 15, wherein the at least one processor isconfigured to: transmit a measurement report based on the detected oneor more measurement events.
 17. The apparatus of claim 15, wherein theat least one processor is configured to: detect that at least one of theone or more triggering conditions are satisfied based on the monitoredone or more first signals; perform a conditional handover to thecandidate target cell based on detecting that at least one of the one ormore triggering conditions are satisfied; and stop the timer based onperforming the conditional handover to the candidate target cell. 18.The apparatus of claim 15, wherein the timer comprises a T312 timer. 19.The apparatus of claim 15, wherein the at least one processor is furtherconfigured to take one or more actions based on the detection that thetimer has expired while monitoring the one or more first signals fromthe candidate target cell for the one or more triggering conditions. 20.The apparatus of claim 19, wherein, in order to take the one or moreactions, the at least one processor is configured to: transition into anidle mode of operation; or initiate a connection re-establishmentprocedure.
 21. The apparatus of claim 15, wherein, in order to stop thetimer, the at least one processor is configured to: receive anindication of a threshold number of in-sync indications; and stop thetimer based on the received indication of a threshold number of in-syncindications.
 22. The apparatus of claim 15, wherein, in order to stopthe timer, the at least one processor is configured to: initiate ahandover procedure to hand the UE over to the target neighbor cell; andstop the timer based on the initiated handover procedure.
 23. Theapparatus of claim 22, wherein the at least one processor is configuredto initiate the handover procedure based on a handover commandinstructing the UE to handover to the target neighbor cell.
 24. Theapparatus of claim 15, wherein, in order to stop the timer, the at leastone processor is configured to: receive a second conditional handovercommand to configure the UE with one or more other candidate targetcell; and stop the timer based on the received second conditionalhandover command.
 25. The apparatus of claim 15, wherein, in order tostop the timer, the at least one processor is configured to: initiate aconnection re-establishment procedure to re-establish a communicationlink between the UE and the serving cell; and stop the timer based onthe initiated connection re-establishment procedure.
 26. The apparatusof claim 15, wherein, in order to stop the timer, the at least oneprocessor is configured to: determine that a second timer is expired;and stop the timer based on the expiration of the second timer.
 27. Theapparatus of claim 26, wherein the second timer comprises a T310 timer.28. An apparatus for wireless communication, comprising: means forreceiving, from a serving cell, a conditional handover command forhanding over the apparatus to a target neighbor cell, wherein theconditional handover command includes one or more triggering conditionsfor executing a handover to a candidate target cell; means for detectingone or more measurement events in one or more measurement objectsconfigured for the serving cell, wherein a timer is configured for theone or more measurement events in the one or more measurement objects;means for starting the timer based on the detection of the one or moremeasurement events in one or more measurement objects configured for theserving cell; means for monitoring one or more first signals from thecandidate target cell for the one or more triggering conditions based onthe detection of the one or more measurement events in one or moremeasurement objects configured for the serving cell; and means forperforming one of: stopping a timer based on performing a conditionalhandover to the target candidate cell; or detecting a timer has expiredwhile monitoring the one or more first signals from the candidate targetcell for the one or more triggering conditions.
 29. A non-transitorycomputer-readable medium for wireless communication, comprising:instructions that, when executed by at least one processor of anapparatus, causes the apparatus to: receive, from a serving cell, aconditional handover command for handing over the apparatus to a targetneighbor cell, wherein the conditional handover command includes one ormore triggering conditions for executing a handover to a candidatetarget cell; detect one or more measurement events in one or moremeasurement objects configured for the serving cell, wherein a timer isconfigured for the one or more measurement events in the one or moremeasurement objects; start the timer based on the detection of the oneor more measurement events in one or more measurement objects configuredfor the serving cell; monitor one or more first signals from thecandidate target cell for the one or more triggering conditions based onthe detection of the one or more measurement events in one or moremeasurement objects configured for the serving cell; and perform one of:stopping a timer based on performing a conditional handover to thetarget candidate cell; or detecting a timer has expired while monitoringthe one or more first signals from the candidate target cell for the oneor more triggering conditions.